[Haskell-cafe] Proposal: Pragma EXPORT

[Evan Laforge]

On Mon, Sep 16, 2013 at 4:09 PM, Wvv <vitea3v at rambler.ru> wrote:
> I suggest to add instead of (or with) export section Pragma EXPORT:

I doubt this has much chance, since haskell already made its choice
here a long time ago (and even if it were still up for discussion,
PRAGMA isn't right for it), but this brings up a design question I've
had.

I too prefer to declare visibility on the declaration rather than in a
separate list.  C doesn't really have a proper module system, but
header files are effectively a separate module signature.  C++ and
Java and go preferred to mark visibility on the declaration.  The ML
family keeps visibility and declarations separate, which is where I
assume haskell got it (that or maybe modula?).  In the case of the
MLs, though, it's a much more developed concept, since they have
module signatures and functors and all that.

In light of haskell's very basic module system, is there any
particular philosophical reason to prefer a separate export list?  Or
are those who prefer it for practical reasons?  The only thing I can
think of is that it provides a nice summary of the module, which
haddock capitalizes on.  But when I want a summary, I look at haddock,
which would already be capable of hiding internal definitions.  I have
heard that haskell's module system was originally intended as a kind
of simple-as-possible placeholder (like records... cough cough), maybe
the designers though an ML-style module system might eventually
materialize?

To me it's always been a hassle to have to jump to the top of the file
and fiddle with the export list, so much so that I tend to leave it
off until a module is pretty stabilized.  It can also be confusing
when the export list is in a different order from the declarations.
Sometimes I want to explicitly mark something private, and simply
"doesn't happen to be in the export list" is too implicit, so I wind
up putting a _ on it.

None of this is a big deal, but I'm curious about other's opinions on
it.  Are there strengths to the separate export list that I'm missing?